The invention relates to a method for operating a steering system of a motor vehicle.
The invention also relates to a computer program and a computer program product with program coding means, in order to carry out such a method for operating a steering system on a computer, especially on a microprocessor, of a control device of the steering system, and to such a control device.
The DE 197 51 125 A1 discloses such a method for operating a steering system, which has superimposing means, which generate an additional angle and superimpose this additional angle on the steering wheel angle specified by the steering handling device. Moreover, the steering wheel angle is superimposed on the movement (additional angle or motor angle) of a control drive, that is, an electric motor, by means of a superimposing gear mechanism (such as a planetary gear). With the help of the superimposing gear mechanism, it is possible to superimpose an additional angle on the steering wheel angle, specified by the steering handling device, in order to increase the driving stability and the comfort, so that variable transformation ratio between the steering wheel angle and the average steering angle of the steerable wheels of the motor vehicle, which depends on the driving dynamics and comfort, is achieved. By these means, it is, for example, possible, from a safety point of view, to restore a motor vehicle, which is threatening to swerve, to a stable driving situation by an appropriate correction of the steering angle. The superimposing means can support other driving dynamics systems (such as an electronic stability program (ESP) or an anti-locking system (ALS). From a comfort point of view, it is also possible, for example, to superimpose a speed-dependent additional angle on a steering wheel angle. By these means, the transformation ratio can be set to a relatively small value at low driving speeds, that is, a relatively small rotation of the steering handling device leads to a relatively large steering angle of the wheels. On the other hand, at high vehicle speeds, a relatively large transformation ratio can be set, so that the driving stability of the motor vehicle is increased.
It is a disadvantage that the steering system itself or the further driving dynamics systems, which are to be supported, are not informed of the actually available dynamics or the functionality of the superimposing means or of the control drive. Even other effects, such as temperature or reaction moments and forces, act on the steering system or control drive. By these means, nominal values for additional angles to be superimposed and additional angular velocities, which cannot be realized by the control drive—whether it be due to a functional disorder or simply because of an actual driving situation (such as the state of the internal combustion engine of the motor vehicle)—of the useful functions of the steering system itself (such as a variable steering ratio) as well as of the further driving dynamics systems could be avoided.